278 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Cambrian Meagher limestone of Weed. The Helena limestone 

 occurs beneath No. i of the Rothpletz section, and may be found, as 

 stated by Weed, near the high school within the city limits and to 

 the north and west in the Kenwood subdivision. It also extends 

 southeast to and beyond the main business street of the city, ending 

 up against the quartz monzonite (qm on map) mass that extends 

 northeast and southwest across the city, cutting off the outcrops of 

 all of the sedimentary formations (see map, pi. 39). 



Reference by me to the Helena limestone, to which Rothpletz 

 refers, is to its outcrops in the upper limits of the city which are on 

 the lower slopes of Mount Helena, and not to the Cambrian lime- 

 stone which forms the cliiTs and steep slopes well up on the mountain 

 side above the city streets. Outcrops of the Helena limestone are 

 best seen in the city in ditches and cellar excavations for houses. 



Rothpletz, after speaking of his reviewing the literature accessible 

 to him, says : * 



Prepared with this information, I began at Helena my investigations, which 

 had as their object to find pre-Cambrian fossils, and before going into the 

 discussion of the fossils which I found there, I will next describe the geologi- 

 cal conditions as, according to my observations, they appear to me to exist. 



The description of his examinations about the city of Helena that 

 follows, clearly indicates that he did not have a clear conception of the 

 pre-Cambian formations exposed in the vicinity of Helena. He con- 

 fuses the Spokane shales and the Marsh shale with the Empire shale, 

 and the Helena limestone with the Cambrian limestones. On page 9,' 

 in speaking of limestones on both sides of the north and south Oro 

 Fino Gulch fault (0-0 on map), which displaces the formations on 

 the lower eastern slopes of Mount Helena, he says that the Flathead 

 quartzite is not exposed on the northwest side of the fault, but 

 "according to its petrographic character, the limestone itself thus 

 corresponds sufficiently to the Helena limestone, as Walcott has 

 described it, so that there can be no doubt as to the identity of both. 

 The oolitic limestone layers are especially characteristic " 



On page ]o,' he states that the northeast slope of Mount Helena 

 above the quarry is constructed exclusively of such Helena lime- 

 stones, up to the terrace-like shoulder, upon which the real summit 

 mass first rises, and upon the shales which occur at the terrace-like 

 shoulder. He describes the summit limestone [dolomite] as having 

 a thickness of 250 meters (8i2-|- ft.), or more. He considers 



^ Rothpletz, p. 8, first new paragraph. 

 ^ Idem, p. 9, line 37, to p. 10. 

 * Idem, p. ID, line 3. 



